Method of electrolytically depositing smooth layers of tin



United States Patent Germany, assignors to Dr. lng. Max Schliitter, Geislingen, Steige, Germany No Drawing. Application January 10, 1957 Serial No. 633,393

Claims priority, application Germany January 16, 1956 18 Claims. (Cl. 204-54) This invention relates to the electrolytic deposition of tin.

Electrolytes for the deposition of layers of tin on wire or broad band steel in modern tin plating plants should yield smooth, properly adhering deposits, as bright and free of pores as possible, with the highest possible cur:

rent densities. Byhigh current densities, at least amps. per square decimetre are understood. -Fast running tin plating plants for band steel require even higher current densities. The said properties must be well defined already in the case of layer thicknesses of 0.3-0.4 In addition it is required that these tin layers should melt onto the wire or band steel with a highly lustring elfect.

To achieve this object, both alkaline and acid tin electrolytes have been used. Alkaline electrolytes having qnadri-valent tin reach only a modest speed of deposition and are therefore hardly practicable for high output plants. Baths of acid electrolytes were used to a fairly large extent based on cresolsulphonic acid with addition of organic sulphones or sulphoxides. These baths permit the very high speeds for the separation oftin, but, owing to the comparatively low'conductivity and high polarisation of the electrodes, they require rather high terminal voltages for electrolytic deposition. Current densities of 20-60 amps. per square decimetre may be achieved with electrolytes which, apart from stannous chloride, contain certain ratherlarge quantities of alkali metal fluorides together with free hydrofluoric acid. These baths also have an advantageously low terminal voltage, but require special care in service, since, owing to the content of acid fluoride, they can lead to serious damage to the skin of the persons working in the plants and, if the baths are insufficiently ventilated, may also lead to damage tothe breathing organs of said persons.

An object of the invention is to produce electrolytes for the deposition of tin which work at low voltages with high current densities and yield smooth deposits of either a thin ora thick metal covering and which can be melted on very well. The electrolytes used in accordance with the invention are easy to maintain and involve no special risks to the health of the operators.

These advantages ,are substantially achieved in that, in accordance with the invention, acid tin electrolytes with additions of flavonols are used. The tin may be present in the electrolytes as fluoborate, sulphate or cresolsulphonate, for example.

Tin electrolytes based on fluoboric acid are known. It is usual for acid tin baths, other than fluoboric acid tin baths, to contain free acid of the same kind as the acid radical in suitable quantity. For depositing a dense,

fine granular deposit, organic additions such as size, gelatine, ,B-naphthol, dihydroxydiphenylsulphone, and dihydroxy-diphenylmethane have already been proposed. With these additions, however, no baths are obtained which yield tin layers which may readily be melted on in only very thin coatings with current densities of 10- 50 amps. per square decimetre, and with them no thick tin layers of 10p thickness and above can be obtained with low current densities without tin bars or tin needles growing out of the deposit.

If, in accordance with the invention, flavonols, particularly those containing several hydroxyl groups, are used as additions to the fluoborate electrolytes, then very eflicient tin baths may be obtained even with a low tin concentration in the electrolyte. As flavonols, quercetin, fisetin, morin and myricetin are concerned, for example. These substances are preferably first dissolved in alcohol and stirred in this form into the electrolytes. The concentration of these additions may be varied within wide limits according to the desired working conditions.

20 mg. quercetin per litre of-bath will prevent the separation of tin bars and tin needles in an electrolyte having 30 g. per litre of tin as fluoborate and 60 g. per litre of free fluoboric acid, and render possible a deposition of tin which, even though still crystalline has excellent .covering power. A further increase of the addition of quercetin to -100 mg. yields a very smooth fine grain and bright tin deposit. A favourable feature in the use of flavonols is the fact that even a large increase of the I added quantities beyond the concentration ascertained to be necessary is not harmful for the deposition elfect. A supply of additives may be addedto the baths sufficient for a longer operating period. Therefore, the limit of solubility of the said additions in the electrolyte may be regarded as the upper limit for making additions.

By combination with other additions the protectiveness of the flavonols may be further intensified. As combined additions polycondensation compounds of ethylene oxide with aliphatic alcohols having an average chain length of about 8-16 carbon atoms are particularly suitable. Such compounds have been used as working agents. On the other hand, polycondensation compounds of ethylene oxide which are known for example as carbowaxes or poly-waxes, are practically without effect. The combination of flavonols with the said substances in many cases makes possible a uniform, smooth deposit of tin over a wide range of current density. Therefore, the property of the tin baths known as throwing power is assisted.

The addition of flavonols is'particularly eflective with tin baths based on fluoboric acid. However, also in the case of-tin baths based on sulphuric acid,*cresolsulphonic acid and stannous chloride-fluoride, flavonols exert a considerable smoothing efi'ect.

The flavonols are preferably added in pure form, bu natural products in which these products are present in appreciable quantity, if necessary, in the form of glycosides and other compound forms, are also efiective in the majority of cases. Thus extracts of fustic may in part replace the action of pure flavonols, even if only to a slight extent. Obviously, the accompanying substances present in this case adversely affect the action I of flavonols. Pure glycosides of flavonols such as querci trin or rutin may be used in higher concentration similarly to pure flavonols.

- The following examples illustrate the possible uses of flavonols in accordance with the present invention:

Example 1 30 per litre of tin as tin fluoborate g. per litre of free fluoboric acid 0.04-02 g. per litre quercetin Example 2 50 g. per litre of tin as tin fluoborate g. per litre of free fluoboric acid 0.04-0.3 g. per litre quercetin I 1.5 g. per litre of a condensation product from ethylene oxide and Cur-C14 316011015 Example 3 50 g. per litre of tin as tin sulphate 60 g. per litre of free sulphuric acid O.l-LO.25 g. per litre morin oxide and lauryl alcohol 0.05-0.25 g. per litre of morin Example 5 40 g. per litre of tin as fluoborate 140 g. per litre of free fluoboric acid 2-3 g. per litre of quercitrin Example 6 35 g. per litre of tin as fluoborate 100 g.,per litre of free fluoboric acid 2 g. per litre of a condensation product from ethylene oxideand lauryl alcohol 1.02.5 g. per litre of rutin From the said baths, according to the tin concentration and the other conditions, deposits may be separated with current densities from l-SO amps. per square decimetre. At the same time high current densities require higher bath temperatures up to 70 C. and movement of the goods to be tin-plated or of the bath. The'highest current densities may be used for producing thin tin coatings such as are used in the tin plate industry. Such deposits may be melted on with a highly lustrous efiect under the usual conditions. For producing thicker tin coatings up to 5 in thickness, low current densities should be selected. Then, under suitable working conditions smooth deposits may be produced up to a thickness of 0.05 mm. and above. I

' We claim:

1. In the electrolytic deposition of tin as a smooth layer, the step comprising depositing said tin from an acid tin electrolyte which contains a flavonol compound in an amount sufilcient to cause deposition of a smooth tin layer and improvement of the throwing power of the electrolyte on operation at low voltages with high current densities.

2. In the electrolytic deposition of tin as a smooth layer, the step comprising depositing said tin from an acid tin electrolyte which contains a fiavonol selected from the group consisting of quercetin, fisetin, myricetin and morin in an amount sufficient to cause deposition of a smooth tin layer and improvement of the throwing power of the electrolyte on operation at low voltages with high current densities.

3. In the electrolytic deposition of tin as a smooth layer, the step comprising depositing said tin-from an acid tin electrolyte which contains a naturally occurring flavonol glycoside selected from the group consisting of quercitrin, rutin and fustic extract in an amount sufticient to cause deposition of a smooth tin layer and improvement of the throwing power of the electrolyte on operation at low voltages with high current densities.

4. In the electrolytic deposition of tin as a smooth layer, the step comprising depositing said tin from an acid tin electrolyte which contains a flavonol compound in an amount sufficient to cause deposition of a smooth tin layer and improvement of the throwing power of the electrolyte on operation at low voltages with high current densities and a polymerisation product of ethylene oxide with an aliphatic alcohol containing at least 6 carbon atoms per molecule.

5. In the electrolytic depositionof tin as a smooth layer, the step comprising depositing said tin from a tin salt solution which contains tin fluoborate, fluoboric acid and a flavonol compound in an amount sutficient to cause deposition of a smooth tin layer and improvement of the throwing power of the tin salt solution on operation at low voltages with high current densities.

6. In the electrolytic deposition of tin as a smooth layer, the step comprising depositing said tin from a tin salt solution which contains tin sulphate, sulphuric acid and a flavonol compound in an amount sufiicient to cause deposition of a smooth tin layer and improvement of the throwing power of the tin salt solution on operation at low voltages with high current densities.

7. In the electrolytic deposition of tin as a smooth layer, the step comprising depositing said tin from a tin salt solution which contains tin cresolsulphonate, cresolsulphonic acid and a flavonol compound in an amount sufiicient to cause deposition of a smooth tin layer and improvement of the throwing power of the tin salt solution on operation at low voltages with high current densities.

8. In the electrolytic deposition of tin as a smooth layer, the step comprising depositing said tin from a tin salt solution which contains tin fluoborate, fluoboric acid and quercetin in an amount suflicient to cause deposition of a smooth tin layer and improvement of the throwing power of the tin salt solution on operation at low voltages with high current densities.

9. In the electrolytic deposition of tin as a smooth layer, the step comprising depositing said tin from a tin salt solution which contains tin fluoborate, fiuoboric acid, quercetin and a condensation product of ethylene oxide with an aliphatic alcohol containing 10 to 14 carbon atoms per molecule, said quercetin being present in said tin salt solution in an amount suflicient to cause deposition of a smooth tin layer and improvement of the throwing power of said tin salt solution on operation at low voltages with high current densities.

10. In the electrolytic deposition of tin as a smooth layer, the step comprising depositing said tin from a tin salt solution which contains tin sulphate, sulphuric acid and morin in an amount suflicient to cause deposition of a smooth vtin layer and improvement of the throwing power of the tin salt solution on operation at low voltages with high current densities.

11. In the electrolytic deposition of tin as a smooth layer, the step comprising depositing said tin from a tin salt solution which contains tin sulphate, sulphuric acid, morin and a condensation product from ethylene oxide and lauryl' alcohol, said morin being present in said tin salt solution in an amount suflicient to cause deposition of a smooth tin layer and improvement of the throwing power of said tin salt solution on operation at low voltages with high current densities.

12. In the electrolytic deposition of tin 'as a smooth layer, the step comprising depositing said tin from a tin salt solution which contains tin fluoborate, fiuoboric acid and quercitrin in an amount suflicient tocause deposition of a smooth tin layer and improvement of the throwing power of the tin salt solution on operation a low voltages with high current densities.

13. In the electrolytic deposition oftin as a smooth layer, the step comprising depositing said tin from a tin salt solution which contains tin fluoborate, fluoboric acid, rutin and a condensation product from ethylene oxide and lauryl alcohol, said rutin being present in said tin salt solution in an amount sufficient to cause deposition of a smooth tin layer and improvement of the throwing power of said tin salt solution on operation at low voltages with high densities.

14. In the electrolytic deposition of tin as a smooth layer, the step comprising depositing tin from an acid tin electrolyte containing at least about 0.02 g./l. of a flavonol compound selected from the group consisting of fiavonols and flavonol glyeosides.

15. An acid tin electrolyte for the electrolytic deposition of a tin layer, said electrolyte containing a tin salt and a fiavonol compound in an amount sufiicient to cause deposition of a smooth tin layer and improvement of the throwing power of said electrolyte on operation at low voltages with high current densities.

16. An acid tin electrolyte for the electrolytic deposition of a tin layer, said electrolyte containing a tin salt and at least about 0.02 g./l. of a flavonol compound.

17. An acid tin electrolyte for the electrolytic deposit-ion of a tin layer, said electrolyte containing a tin salt and at least about 0.02 g./l. of a flavonol compound 0 selected from the group consisting of flavonols and flavonol glycosides.

18. An acid tin electrolyte for the electrolytic deposition of a tin layer, said electrolyte containing a tin salt and at least about 0.02 g./l. of a flavonol compound selected from the group consisting of fiavonols and flavonol glycosides, and a polymerization product of ethylene oxide with an aliphatic alcohol containing at least 6 carbon atoms per molecule.

No references cited. 

1. IN THE ELECTROLYTIC DEPOSITION OF TIN AS A SMOOTH LAYER, THE STEP COMPRISING DEPOSITING SAID TIN FROM AN ACID TIN ELECTROLYTE WHICH CONTAINS A FLAVONOL COMPOUND IN AN AMOUNT SUFFICIENT TO CAUSE DEPOSITION OF A SMOOTH TIN LAYER AND IMPROVEMENT OF THE THROWING POWER OF THE ELECTROLYTE ON OPERATION AT LOW VOLTAGES WITH HIGH CURRENT DENSITIES. 